xid_wraparound tests intermittent failure.

I noticed this when working on the PostgreSQL::Test::Session project I
have in hand. All the tests pass except occasionally the xid_wraparound
tests fail. It's not always the same test script that fails either. I
tried everything but couldn't make the failure stop. So then I switched
out my patch so it's running on plain master and set things running in a
loop. Lo and behold it can be relied on to fail after only a few
iterations.

In the latest iteration the failure looks like this

stderr:
# poll_query_until timed out executing this query:
#
# SELECT NOT EXISTS (
#   SELECT *
#   FROM pg_database
#   WHERE age(datfrozenxid) >
current_setting('autovacuum_freeze_max_age')::int)
#
# expecting this output:
# t
# last actual query output:
# f
# with stderr:
# Tests were run but no plan was declared and done_testing() was not seen.
# Looks like your test exited with 29 just after 1.

(test program exited with status code 29)
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Summary of Failures:

295/295 postgresql:xid_wraparound / xid_wraparound/001_emergency_vacuum
ERROR           211.76s   exit status 29

cheers

andrew

--
Andrew Dunstan
EDB: https://www.enterprisedb.com